Adsorbent-SERS technique for determination of plant VOCs from live cotton plants and dried teas

Authors: PARK, JINHYUK - Texas A&M University; THOMASSON, ALEX - Texas A&M University; GALE, CODY - Texas A&M University; SWORD, GREG - Texas A&M University; LEE, KYUNG-MIN - Texas A&M University; HERRMAN, TIMOTHY - Texas A&M University; Suh, Charles

Submitted to: ACS Omega
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/29/2020
Publication Date: 2/5/2020
Citation: Park, J., Thomasson, A., Gale, C., Sword, G., Lee, K., Herrman, T., Suh, C.P. 2020. Adsorbent-SERS technique for determination of plant VOCs from live cotton plants and dried teas. ACS Omega. 5(6):2779-2790. https://doi.org/10.1021/acsomega.9b03500.
DOI: https://doi.org/10.1021/acsomega.9b03500

Interpretive Summary: Plants release several chemicals in response to insect feeding and damage. These chemicals are commonly referred to as volatile organic compounds and are typically identified or analyzed by gas chromatography/mass spectrometry (GS/MS). Although GC/MS is highly sensitive and accurate, it lacks portability. Consequently, another technology known as Raman spectroscopy has received considerable attention as a portable method for detecting and differentiating chemicals emitted by plants in the field. This technology utilizes a light beam and measures the vibrational characteristics of the chemical to identify or differentiate compounds. The accuracy and sensitivity of Raman spectroscopy can be greatly enhanced if the chemicals are first collected and concentrated on a substrate. This approach is known as surface-enhanced Raman spectroscopy (SERS). We developed and tested a novel material to collect and concentrate plant chemicals for Raman spectroscopy analysis. Our results indicate both qualitative and quantitative differences can be detected by surface-enhanced Raman spectroscopy of our substrate although we find the detection of quantitative differences could be improved. Nevertheless, our findings lay the groundwork for improving or developing substrates which can be used to collect and concentrate chemicals for analysis by Raman spectroscopy. Ultimately, the substrate and Raman spectroscopy could be attached to a drone, tractor, or robot, and easily maneuvered through agricultural fields to rapidly detect the presence of insect pests and feeding damage based on the chemicals released by plants.

Technical Abstract: We developed a novel substrate for the collection of volatile organic compounds emitted from either living or dried plant material to be analyzed by surface-enhanced Raman spectroscopy. We demonstrated that this substrate can be utilized to differentiate emissions from blends of three teas, and to differentiate emissions from healthy cotton plants versus caterpillar-infested cotton plants. The substrate we developed can adsorb volatiles in static headspace sampling environments, and differences in volatile profiles were confirmed with collections on Super-Q resin for dynamic headspace and solid-phase micro-extraction for static head-space sampling followed by gas chromatography to mass spectrometry. Our results indicate that both qualitative and quantitative differences can be detected by surface-enhanced Raman spectroscopy of our substrate although we find the detection of quantitative differences could be improved.